This proposal is to conduct the most complete prospective, longitudinal study of growth and development yet undertaken of children at high risk of obesity. The study of 79 children, now 18-38 months of age, selected on the basis of maternal obesity or leanness, has already achieved two notable successes. (1) It has shown that two independent measures of food intake at 3 months of age predict body size and composition at 1 year. (2) no less important, it has disconfirmed the widely held belief that a low total energy expenditure (TEE) and maternal obesity predict body size and composition at 1 year of age. We now propose to assess the influence on body size and composition at 3, 4 ,5 and 6 years of age of the putative risk factors for obesity that were measured at 3 months of age, are being measured again at 2 years and will be measured again at 4 and 6 years - TEE, REE, food intake and (at 3 months only) infant sucking behavior. In addition, we plan to measure eating behavior, food (especially fat) preferences and those environmental factors that have been proposed as risk factors in order to identify behaviors that can be used in programs of prevention. This effort will be immeasurably enhanced by the ability (for the first time) to assess psychosocial factors in a cohort that has been defined genetically and metabolically as being at high risk for obesity. Data analytic techniques, designed for use with longitudinal data will be used to assess the infulence of the putative risk factors, singly and interactively, on body size and composition. Finally, we plan to bank lymphocytes of the infants and their first degree relatives for future molecular genetic studies.